/Engine/Source/Runtime/Engine/Public/CanvasRendererItem.h
Add a new triangle to the render data. These triangles all use the same transform and material proxy
int32 AddTriangle ( const [FCanvasUVTri](API\Runtime\Engine\Engine\FCanvasUVTri) & Tri, [FHitProxyId](API\Runtime\Engine\FHitProxyId) HitProxyId )